1. Field of the Invention
The present invention relates to an optical disk and an optical disk recording/reproduction device. Specifically, the present invention relates to an optical disk in which information pit arrays are disposed between land tracks and groove tracks in a wobbling manner, and an recording/reproduction device for such an optical disk.
2. Description of the Related Art
Optical disks have excellent removability/portability and random access performance and therefore have been acquiring a broader range of applications in various information equipment fields, e.g., personal computers. As a result, there has been an increasing demand for increasing the recording capacitance of optical disks. Rewritable optical disks require sector-by-sector management of recording and reproduction of data. Therefore, in the production of such disks, address information for each sector is often formed in the form of pits while guide grooves are formed for tracking control purposes. In currently prevalent optical disks, concave and convex tracks of 1-1.6 .mu.m (each width accounting for about 50%) are formed in a spiral shape on a disk substrate. A thin film composed of a recording material (e.g., Ge, Sb, and Te in the case of phase-change type optical disks) is formed on the surface of the tracks by methods such as sputtering. The disk substrate is mass-duplicated in the form of substrates of polycarbonate, etc. by using a stamper which is formed from a master disk in which concave grooves and pits for sector addresses and the like are cut by radiating a light beam. For optical disks having the above configuration, a light beam is radiated on either a concave track or a convex track with a predetermined recording power so as to form marks on the recording film, thereby recording information, and a light beam is radiated on either a concave track or a convex track with a predetermined reproduction power so as to detect light reflected from the recording film, thereby reproducing information.
In recent years, the capacity of information data dealt with in various fields has further increased, so that optical disks are also desired to have increased capacity. Although it is possible to increase the recording density by narrowing the width of each track (hereinafter referred to as the "track pitch"), it is necessary to reduce the track pitch to 1/2 of the conventional track pitch in order to realize a recording density twice as high as the conventional recording density. However, any production method would have a large difficulty in forming a stamper having convex and concave tracks with a stable width which is a half of the track pitch and to duplicate such a disk. On the other hand, there has been proposed a method for increasing the recording density by recording/reproducing information on both the concave tracks and convex tracks. According to this method, a recording density twice as high as the conventional recording density can be realized without changing the width of the concave and convex tracks.
In the case of optical disks in which information is recorded on both convex and concave tracks, providing sector addresses for identifying sectors separately for each track would require forming two addresses or concave tracks at the same time, which would require the use of two or more laser beams and therefore a complex apparatus. Therefore, an intermediate address method has been proposed in which addresses are formed so as to be on both a concave track and a convex track of the optical disk (Japanese Laid-Open Patent Publication No. 6-176404). According to this method, each address on the disk is provided so as to be centered around a boundary line between a convex track and a concave track, with a width substantially equal to that of the concave track, so that the concave track and the convex track share the same address. As a result of this, cutting of the master disk can be facilitated. In this case, however, two tracks are present for the same address when viewed from the recording/reproduction device, and therefore it is necessary to clearly distinguish between them somehow.
Hereinafter, a conventional optical disk and a conventional optical disk recording/reproduction device based on the above-mentioned intermediate address method will be described with reference to the figures.
FIG. 38 is a conceptual diagram showing a conventional optical disk having a sector structure. In FIG. 38, 200 denotes a disk; 201 denotes a track; 202 denotes a sector; 203 denotes a sector address region; and 204 denotes a data region. FIG. 39 is a magnified view of a sector address region and a conceptual diagram showing a conventional intermediate address. In FIG. 39, 206 denotes address pits; 207 denotes recording marks; 208 denotes a groove track; 209 denotes a land track; and 210 denotes an optical disk.
Herein, the groove track 208 and the land track 209 have the same track pitch Tp. Each address pit 206 is disposed so that the center thereof is shifted by Tp/2 along the radius direction of the disk from the center of the groove track 208.
FIG. 40 is a block diagram showing the conventional tracking control and the signal processing of reading signals on an optical disk.
Reference numeral 200 denotes a disk; 201 denotes a track; 210 denotes a light spot; and 211 denotes a disk motor for rotating the disk 200. Reference numeral 212 denotes an optical head for optically reproducing signals on the disk 200. The optical head 212 is composed of a laser diode 213, a collimate lens 214, an object lens 215, a half mirror 216, a photosensitive section 217, and an actuator 218. Reference numeral 220 denotes a tracking error signal detection section for detecting a tracking error signal indicating the amount of dislocation between the light spot 210 and the track 201 along the radius direction. The tracking error signal detection section 220 is composed of a differential circuit 221 and a LPF (Low Pass Filter) 222. Reference numeral 223 denotes a phase compensation section for generating a drive signal for driving the optical head from a tracking error signal; 224 denotes a head driving section for driving the actuator 218 in the optical head 212 in accordance with the drive signal; 225 denotes an addition circuit for signals from the photosensitive section 217; 226 denotes a waveform equivalent section for preventing interference between signs of a reproduced signal; 227 is a data slice section for digitalizing the reproduced signal at a predetermined slice level; 228 denotes a PLL (Phase Locked Loop) for generating a clock which is in synchronization with the digitalized signal; 229 is an AM detection section for detecting AMs (Address Marks); 230 is a demodulator for demodulating the reproduced signal; 231 denotes a switcher for separating the data from the address in the demodulated signal; 232 is a CRC (Cyclic Redundancy Check) determination section for determining errors in the address signal; 233 is an error correction section for correcting errors in the data signal; 234 denotes an address reproduction section composed of elements 225 to 232; and CRC is an error detection code which is generated from an address number and an ID number.
First, positioning control is performed along the focusing direction of the light spot 210, but the description of general focusing control is omitted.
Hereinafter, the tracking control operation will be described. Laser light radiated from the laser diode 213 is collimated by the collimate lens 214, and is converged on the disk 200 via the object lens 215. The laser light reflected from the disk 200 returns to photosensitive sections 217a and 217b via the half mirror 216, whereby the distribution of light amount is detected as an electric signal, which is determined by the relative positions of the light spot 210 and the track 201. In the case of using the two-divided photosensitive sections 217a and 217b, a tracking error signal is detected by detecting a difference between the photosensitive sections 217a and 217b by means of the differential circuit 221 and extracting a low-frequency region of the differential signal by means of the LPF 222. In order to ensure that the light spot 210 follows the track 201, a drive signal is generated in the phase compensation section 223 such that the tracking error signal becomes 0 (i.e., the photosensitive sections 217a and 217b have the same light amount distribution), and the actuator 218 is driven by the head driving section 224 in accordance with the drive signal, thereby controlling the position of the object lens 215.
On the other hand, when the light spot 210 follows the track 201, the amount of reflected light reduces at the recording marks 206 and the address pits 206 owing to interference of light, thereby lowering the output of the photosensitive section 217, whereas the amount of reflected light increases where pits do not exist, thereby increasing the output of the photosensitive section 217. The total light amount of the output of the photosensitive section corresponding to the recording mark 207 and address pits 206 are derived by the addition circuit 225, led through the waveform equivalent section 226, and digitalized at a predetermined slice level at the data slice section 227, i.e., converted into a signal sequence of "0" and "1". Data and a read clock are extracted from this digitalized signal by the PLL 228. The demodulator 230 demodulates the recorded data which has been modulated, and converts it into a data format which allows external processing. If the demodulated data is a signal in the data region, the errors in the data are corrected in the error correction section 233, whereby a data signal is obtained. On the other hand, if the AM detection section 229 detects an AM signal for identifying the address portion in a signal sequence that is constantly output from the PLL 228, the switcher 231 is switched so that the demodulated data is processed as an address signal. The CRC determination section 232 determines whether or not the address signal which has been read includes any errors; if no error is included, the address signal is output as address data.
FIG. 41 shows the states of a reproduced signal (RF signal) and a tracking error signal (TE signal) when the light spot 210 passes the sector address region 203 in the above-described configuration. Although the light spot 210 is located in the center of the track in the data region 204, a drastic dislocation occurs between the light spot 210 and the address pits 206 immediately after the light spot 210 enters the sector address region 203, thereby greatly fluctuating the level of the TE signal. The light spot 210 cannot rapidly follow the address pits 206 but gradually comes closer to the address pits 206, as indicated by the broken line. However, since the sector address region 203 is short, the data region 205, which is a grooved region, is reached before the light spot manages to completely follow the address pits 206, so that a tracking control is performed so that the off-tracking Xadr is eliminated in the grooved region. Moreover, since a portion of the light spot 210 is on the address pits 206, an RF signal as shown in FIG. 41 is obtained. The RF signal amplitude Aadr varies in accordance with the distance between the light spot 210 and the address pits 206. Specifically, Aadr decreases as the distance becomes larger, and increases as the distance becomes smaller.
However, in accordance with the sector address having the configuration shown in FIG. 39, the distance between the light spot and the address pits may also vary in the sector address region in the case where the center of the light spot is dislocated from the center of the track in the data region. As a result, there is a problem in that, although the amplitude of the reproduced signal in the address pit region would increase if the light spot shifted closer to the address pits, the amplitude of the reproduced signal in the address pit region would decrease if the light spot shifted away from the address pits, thereby resulting in an insufficient reading of the address.
There is also a problem in that, since the light spot is dislocated from the address pits in the sector address region, a large fluctuation in level (which does not indicate the actual track offset amount) occurs in the tracking error signal. Since the tracking control is performed by employing such a tracking error signal, a tracking offset occurs after the light spot passes the sector address section.
There is also a problem in that, since the same address pits are allocated to a land track and its adjoining groove track, it is impossible to identify whether or not a track which is currently being followed is a land track or a groove track.